The present invention relates to a zoom mechanism for a zoom lens in cameras and the like, and more particularly, to a zoom mechanism for a zoom lens in still cameras, video cameras and the like.
An example of a conventional zoom mechanism for a zoom lens in cameras and the like will be describedd hereinafter in connection with a zoom lens composed of two lens groups shown in FIGS. 5A and 5C and FIG. 6. FIGS. 5A and 5C respectively show conditions where a zoom lens is at its wide-end (the end of a wide anagle side) and is at its tele-end (the end of a telephoto side). FIG. 5B shows an amount of movement of lens groups L1 and L2 in a zooming operation. FIG. 6 is an expanded view of essential parts of the zoom mechanism shown in FIGS. 5A and 5C.
First and second lens groups L1 and L2 are fixed to respective first and second lens group holding frames 31 and 32. The first lens group holding frame 31 is threadably engaged with a rectilinear motion frame 33 by means of helicoid threads and the first lens group holding frame 31 is adapted to move in a direction of the optical axis of the first lens group by rotating the holding frame 31 relative to the rectilinear motion frame 33 in a focusing operation to change its focused position.
The rectilinear motion frame 33 and the second lens group holding frame 32 are movably fitted in a fixed frame 35. In addition, the rectilinear motion frame 33 and the second lens group holding frame 32 are respectively provided with driving pins 33a and 32a. The pins 33a and 32a pass through an elongated groove 35a which is provided on the fixed frame 35 in a direction of the optical axis such thata their circumferential rotations are prevented and fit in respective driving cam grooves 36a and 36b which are provided on an operating ring 36.
The fixed frame 35 is secured to a camera body (not shown).
With such arrangement, when the operating ring 36 is rotated in a direction shown by an arrow a in FIG. 6, the rectilinear motion frame 33 and the second lens group holding frame 32, whose rotations are limited by the fixed frame 35, move respectively along the cam grooves 36a and 36b in a direction of the optical axis from the condition showon in FIG. 5A to that showon in FIG. 5C with a zooming operation such that the first lens group L1 moves from a position P1 along a curve x to a position P1' and the second lens sgroup L2 moves from a position P2 along a curve y to a position P2' as shown in FIG. 5B.
As such, in a conventional zoom mechanism it is required that the rectilinear motion frame 33 and the second lens group holding frame 32 move separately along the respective cam grooves 36a and 36b during a zooming operation and the first lens group holding frame 31 moves in relation to the rectilinear motion frame 33.
Accordingly, the increase of the number of the number of lens groups necessitates the provision of complicated mechanisms.